Configs per step

[hoegaarden]

What this PR does / why we need it:

This allows finer grained configurations of an app's template steps from a pkgi.

• values in a pkgi can be configured to be be attached to a specific template step in the resulting app
• configuration of an app's template step, through annotations on the pkgi, can be configured to apply to a specific templating step

Which issue(s) this PR fixes:

Related issues / comments:

• Seeking clarification on PackageInstall values. #1461 (comment)
• **Explore:** Package authors should be able to customize how InstalledPackage values get included in templating steps #122

Does this PR introduce a user-facing change?

First off: the previous behavior regarding values and annotations should have kept the same, so this should be fully backwards compatible.

It introduces a couple of new and additional knobs:

• pkgi.spec.values.templateSteps is an []int
  • it's optional and default to an empty list, which then behaves like before this change
  • pkgi.spec.values.templateSteps: [ 0 , 2 ] would attach this value secret as a value to the first and third template step
  • if a template step does not take values, or a non-existing template step is referenced, an error is produced
• In addition to the already existing annotations¹, new ones² have been introduced, modeled after the "fetch secret annotation"³:
  • e.g. in addition to ext.packaging.carvel.dev/helm-template-name which applies to the first helm template step, ext.packaging.carvel.dev/helm-0-template-name can be used to explicitly target the first template step
  • if for a referenced template step the annotation is not relevant (a "helm annotation" for a ytt template step), the annotation is ignored, i.e. no error is produced
  • the original annotations are still used (for the first relevant templating step), again keeping the current behavior

Note: A user deploying a pkgi would still need to understand the implementation details of the pkg, i.e. which template steps it consists off, which values a certain step takes, ...

Additional Notes for your reviewer:

Review Checklist:

• Follows the developer guidelines
• Relevant tests are added or updated
• Relevant docs in this repo added or updated
• Relevant carvel.dev docs added or updated in a separate PR and there's
  a link to that PR
• Code is at least as readable and maintainable as it was before this
  change

Additional documentation e.g., Proposal, usage docs, etc.:

Footnotes

1. ext.packaging.carvel.dev/helm-template-name
ext.packaging.carvel.dev/helm-template-namespace
ext.packaging.carvel.dev/ytt-paths-from-secret-name
ext.packaging.carvel.dev/helm-template-values-from-secret-name
ext.packaging.carvel.dev/ytt-data-values-overlays ↩

2. ext.packaging.carvel.dev/helm-%d-template-name
ext.packaging.carvel.dev/helm-%d-template-namespace
ext.packaging.carvel.dev/ytt-%d-paths-from-secret-name
ext.packaging.carvel.dev/helm-%d-template-values-from-secret-name
ext.packaging.carvel.dev/ytt-%d-data-values-overlays ↩

3. ext.packaging.carvel.dev/fetch-%d-secret-name ↩

[praveenrewar]

@hoegaarden Thank you so much for working on this and apologies for not being able to look into it.
I will try to take a closer look at the PR next week, however, would you be open to creating a proposal for this for the maintainers to review. Once the proposal is approved, we can move forward with implementation. Also, feel free to join our community meetings and discuss it there.

[hoegaarden]

would you be open to creating a proposal

Sure. I'll try to wip up a PR for a proposal the next couple of days.